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Author Topic: attention color whizes: non-typical sRGB/RGB/ProPhoto question  (Read 228714 times)

digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #60 on: January 02, 2011, 02:16:35 pm »

Listen: I don't think you are in a mood to learn this stuff. I can make an error and everybody including Bruce also can make a mistake. So making a mistake is not the point. The point is that you are not showing any indication to learn what I have been trying to tell you. I can only do so much effort. I don't think it is going forward. It is up to you if you want to take it forward.

Look, I’m going to start here and go backwards, then I’m bowing out because your attitude, language and efforts here have progressively convinced me you are wasting my time and others. If your idea of educating us is dismissing what we suggest, ignoring questions posed and acting like a bonehead, yes, I’d prefer not to learn from you. Lets start with this:

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How about this, the clock is ticking on you getting clarification from Bruce about all this.

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We can keep it between you and me.

Now why would we want to do that? What are you afraid of hearing from Bruce that shouldn’t be shared in this post? That attitude leaves me suspicious of your motives, example 1.
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Oh come on. I have provided graphs that I drew showing the Adobe and Prophoto primaries, written detailed and long messages on how to interpret white points, how to generate other coordinate systems in the same 3D color space. I don't think you are being fair here.

Why should I take your one drawing as fact when the half a dozen other utilities I have, that plot the gamuts disagree with your concept? Why are you making no effort to use the utilities and actual profiles that define the gamuts? Example 2.
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I have not seen what Bruce's gamut is showing. I tried it on my Mac but it was not loading with my firefox browser. I don't know why.

So you are on a Mac, and you can’t even launch the browser that does work and shipped with your Mac, Safari? Nor can you also launch the ColorSync utility, also part of the Mac utilities that would again allow you to plot the gamuts of the two color spaces. You are making zero effort to see what multiple utilities built for theses tasks all agree upon. Example 3.
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I suspect that is what is going on here and perhaps in Bruce Lindbloom's graph (though I have yet to see them.) I suspect that he might have done what MarkM has done above with his calculation.

So in addition to (presumably) all the various gamut mapping utilities being wrong, myself and others in agreement about the gamut of the two spaces, Mark being wrong, Sandy being wrong, now Bruce is wrong too? Example 4.
But you are correct and we are to take the illustration you built as proof of concept?

You can use a different browser and view Bruce’s plots and again, take up his “errors” with him which you don’t see to want to do. You can view the gamuts in the Colorsync Utility. You can download a demo of ColorThink which in that mode WILL plot the 3D gamuts of the two spaces discussed. At such a point, can you tell us, yes or no, where you see Adobe RGB (1998) exceeding the gamut of ProPhoto RGB anywhere in color space? If not, as the rest of us can clearly see, are you suggesting that Adobe, the profiles, the gamut viewers, the color scientist and his site are wrong, but the illustration you built, IS correct? Otherwise, this is just an exercise in you expressing verbal diarrhea, a process I no longer wish to be part of.




« Last Edit: January 02, 2011, 03:09:49 pm by digitaldog »
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #61 on: January 02, 2011, 02:28:14 pm »

Lab 30|69|-114 is also the highest saturated blue of AdobeRGB.

Hi,

XYZ=[0.188185   0.075274   0.991108] is the highest saturated blue in Adobe RGB (D65). Its representation in Propho (D50) is RGB = [0.183388   0.031393   1.201037].

You double check that using Bruce Lindbloom' matrix for conversion from Prophoto RGB to XYZ:


0.79767   0.13519   0.03135
0.28804   0.71187   0.00009 * [0.183388   0.031393   1.201037]' = [0.188185   0.075274   0.991108].
0.00000   0.00000   0.82521


You see that 1.20, which means that 1.20 times the unit stimuls of Prophoto blue primary will be required to match it so it is clipped in Prophoto (D50). I hope you see it now. And, it would appear this is what your first image shows.

Joofa
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #62 on: January 02, 2011, 02:39:56 pm »

Why don't you see any color shift when you convert a pure white from ProPhotoRGB to AdobeRGB and vice versa?

If I am understanding correctly,

1. 'pure white' in one, with its native illuminant, does not have the same XYZ coordinates as 'pure white' in the other, in its native illuminant; at least when, as in this case, the native illuminants used to specify the two color spaces differ.  
2. Part of the point of chromatic adaptation is to map whites from different illuminants to one another (providing three constraints on the nine components of a 3x3 adaptation matrix).
3. Part of color space conversion must involve chromatic adaptation, otherwise there will be a color shift.
4. I would presume that Photoshop works internally with colors already adapted to a common illuminant, as Joofa is doing.  Otherwise, in the short integer representation they use, white in some color spaces might be out of the 16-bit data range, resulting in white not being representable in some color spaces.  It would make much more sense to adapt everything to say D50.  If I am understanding correctly, this is what Joofa is calling AdobeRGB (D50).  It is not the same as the AdobeRGB (1998) spec, it will be as close as the chromatic adaptation allows.  Does anyone know if this is how Adobe does things (and can tell)?
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tho_mas

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #63 on: January 02, 2011, 02:49:52 pm »

XYZ=[0.188185   0.075274   0.991108] is the highest saturated blue in Adobe RGB (D65).
Lab 30|69|-114 is also the highest saturated blue of AdobeRGB.
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digitaldog

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #64 on: January 02, 2011, 03:07:06 pm »

Does anyone know if this is how Adobe does things (and can tell)?

According to Chis Cox there:
 
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Which Illuminant type does Adobe use to define their LAB color space data?

D50 / 2 degree --- same as the ICC V2 CIE LAB PCS definition.
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #65 on: January 02, 2011, 03:07:44 pm »

Lab 30|69|-114 is also the highest saturated blue of AdobeRGB.

What is that supposed to mean?
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sandymc

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #66 on: January 02, 2011, 03:11:32 pm »

Does anyone know if this is how Adobe does things (and can tell)?

The internal space is Prophoto primaries, D50, linear light (aka gamma =1). Readouts e.g., on Lightroom, however have an sRGB gamma curve.

Sandy
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #67 on: January 02, 2011, 03:25:34 pm »

If I am understanding correctly,

Hi Emil,

Nice to see you here. Well you always understand correctly. :D

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1. 'pure white' in one, with its native illuminant, does not have the same XYZ coordinates as 'pure white' in the other, in its native illuminant; at least when, as in this case, the native illuminants used to specify the two color spaces differ.  

Yes, because in their native spaces, both have tristimulus [1,1,1], but in absolute terms (XYZ) they represent different colors.

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2. Part of the point of chromatic adaptation is to map whites from different illuminants to one another (providing three constraints on the nine components of a 3x3 adaptation matrix).

Yes, say so D65 white [0.95, 1, 1.08] goes to D50 white [0.96, 1, 0.83]. In their respective spaces both have representation [1,1,1]. But they differ in XYZ, of course, i.e.,

(a) [0.95, 1, 1.08] in D65 space has tristimuls [1,1,1].
(b) [0.96, 1, 0.86] in D50 space has tristimuls [1,1,1].
(c) [0.95, 1, 1.08] in D50 does not have tristimuls [1,1,1] <------------ This causes confusion for some.
(d) [0.96, 1, 0.86] in D65 does not have tristimls [1,1,1] <------------ This causes confusion for some.

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3. Part of color space conversion must involve chromatic adaptation, otherwise there will be a color shift.

Color spaces are related by an affine transformation (okay linear). That is all that is needed. What many don't  realize is that if the color space primaries are kept the same but the white point is moved, then that affine transformation is identified by a fancy name - Bradford/von Kries/etc- like chromatic adaption.

A color space is just a vector space. Given any 3 linearly independent bases (RGB) one cay figure out the coordinates in a different set of RGB basis. White point is only used to set the length of "unit vector" as I explained here:

http://www.luminous-landscape.com/forum/index.php?topic=49940.msg412251#msg412251

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4. I would presume that Photoshop works internally with colors already adapted to a common illuminant, as Joofa is doing.  Otherwise, in the short integer representation they use, white in some color spaces might be out of the 16-bit data range, resulting in white not being representable in some color spaces.  It would make much more sense to adapt everything to say D50.  If I am understanding correctly, this is what Joofa is calling AdobeRGB (D50).  It is not the same as the AdobeRGB (1998) spec, it will be as close as the chromatic adaptation allows.  Does anyone know if this is how Adobe does things (and can tell)?

Digital Dog has mentioned that Adobe is using D50 space in Photoshop. So, I think that will correspond to the following situation in my original note:

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Joofa wrote on DPReview:


Fraction of unit stimulus blue ProPhoto RGB primary needed to match unit stimulus blue Adobe RGB primary:

(3) Adobe RGB white point=D50, PropPhoto RGB white point=D50, Fraction needed=0.88

This is the same mode for which I think MarkM did is calculation after Bradford transformation. So you won't see the clipping in this mode, unless the Adobe RGB (D65) blue primary is correctly figured out after Bradford, and which is no longer [0,0,1].

Sincerely,

Joofa
« Last Edit: January 02, 2011, 03:29:57 pm by joofa »
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #68 on: January 02, 2011, 04:10:34 pm »


Color spaces are related by an affine transformation (okay linear). That is all that is needed. What many don't  realize is that if the color space primaries are kept the same but the white point is moved, then that affine transformation is identified by a fancy name - Bradford/von Kries/etc- like chromatic adaption.


I would have thought the primaries are also shifted by the chromatic adaptation transformation; after all it is a linear map.  

The R,G,B primaries define a parallelepiped in linear XYZ space with the white point W at its tip, and R,G,B defining other corners of the parallelepiped; in terms of their vector coordinates, W=R+G+B.  If W changes, then the R,G,B primaries do as well.  Could the whole issue here be that the XYZ parallelepipeds differ for AdobeRGB (natively D65) and its adaptation to D50, and that the native B primary for AdobeRGB, as a point in linear XYZ space, lies outside Prophoto (natively D50), while the adapted B primary for AdobeRGB (ie mapped to D50) lies within Prophoto?  That would be consistent with what I've read so far of this thread (admittedly not a lot), where you are claiming that it does lie outside, while others are looking at gamut viewers like the one on Bruce Lindbloom's site and seeing that Prophoto contains AdobeRGB.  But the disclaimer on Lindbloom's site is that all the gamuts shown in the viewer have been adapted to D50.
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #69 on: January 02, 2011, 04:25:12 pm »

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What is the representation of the color XYZ=[0.188185   0.075274   0.991108] in standard Prophoto (D50) color space?

This seems to be the crux of the question, so I will try again.

Your numbers [0.188185   0.075274   0.991108] in XYZ space are going to look different depending on the chromatic adaptation of the viewer. Those numbers are assuming a white point that corresponds to D65. If you want to preserve the color appearance when viewed under D50 you need to account for chromatic adaptation. Using Bradford you get a new set of XYZ numbers: [ 0.14922403  0.06321976  0.74483862].

So now you can say [0.188185   0.075274   0.991108] under D65 will appear the same as [ 0.14922403  0.06321976  0.74483862] under D50. Now you are free to translate to ProPhoto space and preserve appearance. You will get (as I explained above) [  88   36  241 ].

So the answer to you question quoted above is: [88 36 241]

This matches exactly what you get from photoshop. Consider that before you tell me I'm wrong. You seem to be prepared to say Andrew is wrong, I'm wrong, Adobe is wrong, ColorThink is wrong, etc. and in all this time YOU are the only one who has noticed.

This is really very simple: you are going from one space with one white point to a different space with a different white point. There is no problem here.


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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #70 on: January 02, 2011, 04:30:51 pm »

I would have thought the primaries are also shifted by the chromatic adaptation transformation; after all it is a linear map.  

The R,G,B primaries define a parallelepiped in linear XYZ space with the white point W at its tip, and R,G,B defining other corners of the parallelepiped; in terms of their vector coordinates, W=R+G+B.  If W changes, then the R,G,B primaries do as well.  

Hi Emil,

The case I'm mentioned in that particular message above is where the primaries are kept the same in chrmacity coordinates. Which means that the direction of primaries in 3D are the same. Now if the white point changes, each primary is scaled by a different number so that they become the new "unit stimulus" primary. Think of it like a diagonal matrix multiplication with the matrix of original primaries - direction remain the same, but magnitudes get scaled.

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Could the whole issue here be that the XYZ parallelepipeds differ for AdobeRGB (natively D65) and its adaptation to D50, and that the native B primary for AdobeRGB, as a point in linear XYZ space, lies outside Prophoto (natively D50),

Yes.

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while the adapted B primary for AdobeRGB (ie mapped to D50) lies within Prophoto?  T

Exactly. Glad you are a sane voice here  :D

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hat would be consistent with what I've read so far of this thread (admittedly not a lot), where you are claiming that it does lie outside, while others are looking at gamut viewers like the one on Bruce Lindbloom's site and seeing that Prophoto contains AdobeRGB.  But the disclaimer on Lindbloom's site is that all the gamuts shown in the viewer have been adapted to D50.

I think the situation is becoming clearer now they are adpated to D50 gamuts that is why they don't show the clippings in Prophoto RGB (D50).

Thanks,

Joofa
« Last Edit: January 02, 2011, 04:35:43 pm by joofa »
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #71 on: January 02, 2011, 04:33:15 pm »

Consider that before you tell me I'm wrong. You seem to be prepared to say Andrew is wrong, I'm wrong, Adobe is wrong, ColorThink is wrong, etc. and in all this time YOU are the only one who has noticed.

Is there any issues with you guys here? Do you have a bad day today. First digital dog went berserk and now you are putting words in my mouth (when did I say Andrew/ColorThink/ etc. are wrong with the wording you seem to suggest.

Look, I'm here to get educated and also contribute my bit. I can make mistakes. Anybody can. Please be patient.

Joofa
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ejmartin

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #72 on: January 02, 2011, 05:12:29 pm »

Hi Emil,

The case I'm mentioned in that particular message above is where the primaries are kept the same in chrmacity coordinates. Which means that the direction of primaries in 3D are the same. Now if the white point changes, each primary is scaled by a different number so that they become the new "unit stimulus" primary. Think of it like a diagonal matrix multiplication with the matrix of original primaries - direction remain the same, but magnitudes get scaled.

From what I understand reading Lindbloom's site, this is true for one form of chromatic adaptation (what he calls XYZ scaling).  The other transformations (eg Bradford, which he uses for his considerations) involve a more non-trivial linear transformation on the coordinates.

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I think the situation is becoming clearer now they are adpated to D50 gamuts that is why they don't show the clippings in Prophoto RGB (D50).

Which begs the question, why would one be interested in comparing the primaries for two gamuts under different illuminants, without adaptation?  It's a little like saying that the blues can be clipped when using a too low value of the color temp in an image.  Well, yes, but so what?
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #73 on: January 02, 2011, 05:13:26 pm »

Joofa, the mistake you are making is very simple: when you are using the RGB -> XYZ matrices you are not accounting for the different reference white points. Bruce Lindbloom is explicit about this in the implementation notes. (read note number 2 here: http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html )

You are plotting converted RGB values on the same XYZ graph without accounting for the different white points. If you account for the different white points, your problems go away. If you don't, you are comparing apples and oranges.

In case you don't feel like clicking on the link, here is Bruce's implementation note for using the matrices:
"Be careful that reference whites are used consistently. For example, sRGB is defined relative to a D65 reference white and ICC profiles are defined relative to a D50 reference white. Mismatched reference whites must be accounted for elsewhere, typically by using a chromatic adaptation algorithm."
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #74 on: January 02, 2011, 05:26:14 pm »

From what I understand reading Lindbloom's site, this is true for one form of chromatic adaptation (what he calls XYZ scaling).  The other transformations (eg Bradford, which he uses for his considerations) involve a more non-trivial linear transformation on the coordinates.

No, no not at all. The situation I described is not XYZ scaling. That is the wrong transform!

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Which begs the question, why would one be interested in comparing the primaries for two gamuts under different illuminants, without adaptation?  It's a little like saying that the blues can be clipped when using a too low value of the color temp in an image.  Well, yes, but so what?

Emil, if you keep the same chromacity coordinates but change the white point, the diagonal scaling I talked about is not XYZ scaling. Please write the equations for these transformations it will be clear to you.

Joofa
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joofa

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #75 on: January 02, 2011, 05:30:17 pm »

Joofa, the mistake you are making is very simple: when you are using the RGB -> XYZ matrices you are not accounting for the different reference white points.


Mark, trust me I have taken white point into accounts. Please see one of my responses to Emil above. The original Adobe RGB (D65) blue primary falls outside the Adobe (D50) space (I like Emil's word parallelepiped here) you get after color adaptation.

Joofa
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #76 on: January 02, 2011, 06:06:53 pm »

Joofa, you keep trying to show that the color [0, 0, 1] in Adobe1998 clips in the ProPhoto space.

I, and others, and photoshop say it doesn't. I even showed you the math. In ProPhoto that color is [88 36 241]. It doesn't clip.

So a simple question: are we wrong?
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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #77 on: January 02, 2011, 07:16:04 pm »

I must say I'm quite intrigued as to the outcome here. I'm no color scientist, far from it, but I'd like to know why, in the Apple Color Synch Utility, Adobe(1998) is depicted as entirely within ProPhotoRGB (as i'd expect) and yet if I view the same profiles in ColorThink 2.2 there is a clear difference, the Adobe(1998) blue primary is outside the ProPhotoRGB space. I don't have ColorThink V3Pro to compare with.
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MarkM

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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #78 on: January 02, 2011, 07:26:55 pm »

Nick, I don't have 2.2 to compare, but I've attached the graph from ColorThink 3 showing the Adobe98 (red wireframe) with the ProPhoto (colored wireframe) in xyY Obviously a little hard to see when you can't spin it, but adobe98 is completely inside the prophoto space.
« Last Edit: January 02, 2011, 07:29:48 pm by MarkM »
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Re: attention color whizes: non-typical sRGB/RGB/ProPhoto question
« Reply #79 on: January 02, 2011, 07:29:49 pm »

Joofa,

This can basically be illustrated in Photoshop as well:

with a Granger Rainbow in Adobe RGB, and a customized Proof setup to ProPhoto RGB while using the Absolute Colorimetric rendering intent, the Gamut Warning will indicate massive clipping of blue hues as well as of close-to-white colors. Right the way as given in 3D below. Of course, the out-of-gamut marks disappear when changing the Proof setup to RelCol rendering.

In case it doesn't work - which may depend on the Photoshop version used - go to Color Settings and change the Color Engine from Adobe ACE to Microsoft ICM [which is offered when running Photoshop on a Windows platform; no idea about Macs].

Peter

Secondly, I don't know how tho_mas produced the following diagram, but isn't that saying the same thing? Though he thoght otherwise. He said that it is showing profiles. But it seems like blue is projecting out of the mesh.  I am no expert in such programs and some of the associated terminology, so may be it is showing something else.

This is the shape of the profiles (abscol to D50; Adobe = white)... but this is just the shape of the profiles, totally independed from any real application:




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